In a system for transmitting high-frequency signals, for example, millimeter wave or microwave signals through a waveguide cable, it is necessary to connect a feed line to the waveguide cable on a circuit board. For this connection, a dielectric waveguide-microstrip transition structure is conventionally used (e.g., see Patent Document 1). The dielectric waveguide-microstrip transition structure has a dielectric waveguide containing a dielectric block and a conductor film covering an entire surface thereof, except for a signal input/output portion. In the dielectric waveguide, a slot is formed in a bottom surface to extend in a direction perpendicular to a traveling direction. The dielectric waveguide is mounted on the circuit board via a spacer.
Patent Document 1: Japanese Patent Application Laid-open No. 2010-141644